Perception and other cognitive functions such as planning, thought and learning reflect processing of complex information by the cerebral neocortex. Adaptive function depends critically on inputs from subcortical centers and on subsequent signal processing by appropriately organized cortical microcircuits. The proposed work asks how information is faithfully transferred from one part of the brain to the next and how signal-transforming feedforward networks become refined by developmental experience. Using the rodent whisker-to-barrel system, we will examine thalamocortical microcircuits in normally- reared animals and in animals raised with abnormal tactile experience produced by simple trimming of whisker hairs during early postnatal life. Using quantitative sensory physiology methods and single-cell recordings, including anatomical labeling of functionally characterized thalamocortical neurons, we will evaluate hypotheses derived from a long-standing model of thalamocortical function in somatosensory and visual systems. The model postulates that response tuning of cortical layer 4 neurons reflects specific thalamic inputs and that local circuitry dynamically adjusts receptive field properties by regulating overall network excitability. Specific experiments will investigate the innervation pattern of thalamocortical axons, their functional impact, and their experience-dependent developmental plasticity. Results are expected to establish key mechanisms of thalamocortical function and development shared by different systems in different species.